1. Field of the Invention
The present invention relates to an oxygen gas production apparatus by which high purity gaseous oxygen can be expediently produced.
2. Description of the Prior Art
It is customary to produce oxygen gas in an air fractionation plant which separates oxygen from nitrogen by taking advantage of their difference in boiling point. This conventional air fractionation plant is provided with an expansion turbine for generating the refrigeration necessary for the liquefaction and fractionation of air, which utilizes the Joule-Thomson effect due to adiabatic expansion.
However, because of its extremely high speed (tens of thousand revolutions per minute), the expansion turbine cannot delicately follow variations in demand load (variations in the rate of withdrawal of product oxygen gas). Thus, it is technically difficult to vary the rotational speed of the expansion turbine quickly and accurately in response to changes in the demand for product oxygen gas so as to maintain the compressed material air at a constant temperature at all times. As a result, a variation is inevitable in the purity of product oxygen gas, for low purity oxygen is frequently outputted to depress the overall purity of product oxygen.